1. Field of Invention
The present invention relates to an apparatus for conditioning pressure molded plastic articles that incorporates a variety of linearly interconnected operating sections for the performance of processing steps synchronously with an in-feed from a machine having an intermittent output and a discharge into another machine that requires a similarly intermittent in-feed. In particular, the apparatus of the present invention accommodates operations intermediate between the production of plastic preforms and their transformation into hollow articles, such as bottles and the like, according to the well known process of blow-molding bi-axially oriented plastic containers.
2. Description of the Prior Art
Conventionally, when intermediary processing operations have to be interposed between two disparate manufacturing steps, the tendency is to avoid performing the latter, as well as the intermediary operations, in synchronism due to difficulties in constructing corresponding apparatus and to control the several processing steps that may be involved. This applies particularly to the production of molecularly oriented plastic articles, as for example containers made of orientable plastics, such as polyethylene terephthalate (PET), other polycondensation resins and polyolefins.
Bi-axially oriented plastic containers are usually produced using either a two stage, or single stage process, both of which have disadvantages.
In the two-stage process, parisons are produced by extrusion, preferably in an injection molding machine, cooled to room temperature, stored and conveyed in bulk to a re-heat and blow machine. The two operations are not synchronous, their respective outputs differ and their combined performance wastes energy.
In the single-stage process, the operations of injection molding and blow molding are combined within one machine in which the parisons are indexed in conventional ways from one to the other, in effect eliminating the need to convey them. However, this is accomplished at the expense of accurate control of the process parameters, such as the temperature distribution within the parisons and also, with but a minimum of possible intermediate processing steps that are increasingly called for. Thus, the single-stage process is limited to relatively simple products and low outputs, the latter because of design limitation of the typical single-stage apparatus.
It is highly desirable and an objective of the present invention to develop a continuous, synchronous system for conditioning pressure molded plastic articles and preferably for preparing hollow plastic articles from injection molded plastic parisons especially capable of transferring to a blow molding machine the entire output of an injection molding machine while adjusting the temperature thereof, or otherwise conditioning on-line the entire output so as to obtain desired morphology and physical properties in the blown oriented hollow plastic articles in an uninterrupted, synchronous operating cycle which is independent of the number of the required conditioning stages.
It is a still further objective of the present invention to perform a crystallizing operation of PET within the said cycle.
It is particularly desirable and a further objective of the present invention to accommodate in the aforesaid system parisons having axially variable wall thickness which therefore present particular temperature conditioning problems.
An additional objective is to adapt the output of the injection molding machine and that of the intermediate operations to the pace at which the blow molding machine is capable of processing parisons.
An additional objective is to accomplish the foregoing while varying the center spacing of the parisons from the closer center spacing of the injection molding apparatus to the wider center spacing of the blow molding apparatus.
Further objects and advantages of the present invention will appear hereinbelow.